1. Field of the Invention
The present invention relates to a phase-change optical disc recording method, in particular, to a method for determining an optimum recording LD (Laser Diode) power to be used in a phase-change optical disc recording. The phase-change optical disc recording is, for example, recording information on a phase-change optical disc from which a conventional CD (compact disc) player and a conventional CD-ROM drive apparatus can read data.
Further, the present invention relates to an information recording and reproducing apparatus and method for optically recording information in and reproducing information from a recording medium. In particular, the present invention relates to an optical disc (such as a phase-change optical disc) recording apparatus which controls the recording device (such as an LD) power to be an optimum one. The phase-change optical disc recording apparatus is, for example, a phase-change optical disc recording apparatus which can also read data from a CD and a CD-ROM.
Further, the present invention relates to a recording pre-compensation method for achieving a desired-shaped mark formed in a recording medium.
2. Description of the Related Art
Optical discs can be classified into WORM (Write Once, Read Many) ones and rewriteable ones. The rewriteable discs can further be classified into magneto-optical discs and phase-change discs. For the phase-change discs, a phase-change recording technique is used. In the technique, data is recorded by using two transition phases of a recording layer metal of such a disc, which phases are an amorphous phase and a crystal phase. The reflectivity is different between the two transition phases and this property of the recording layer metal is used for the data recording.
Japanese Laid-Open Patent Application No.63-25408 discloses an optical disc recording method in the related art. In this system, an optimum value of a recording light intensity is determined. Further, in order to keep a good recording quality, a recording light intensity is varied for recording initially. Then, a thus-recorded signal is reproduced and a recording light intensity which results in a good state of the reproduced signal is determined as being the above-mentioned optimum recording light intensity. Then, the recording light intensity is controlled to be the optimum one and actual signal recording is performed. In other words, before starting actual signal recording, a trial is performed so as to determine the optimum recording power.
With regard to optical disc recording, a sensitivity of a recording medium and/or a light emitting power of a recording LD (Laser Diode) may be degraded due to time elapsing and dust/dirt adhering thereto. The degradation should be compensated for so as to perform data recording in an optimum condition. One method of compensating for this degradation is to perform the above-described trial so as to determine the optimum recording power. In a standardized optical disc, a trial writing region is provided in a medium format. This region is used for trial writing using a varying recording LD power before recording actual data. Then, a signal thus recorded in the region is reproduced and an optimum recording condition is determined using the reproduced signal. Then, the actual data recording is performed using the thus-obtained optimum recording condition.
With regard to phase-change optimum disc recording, such trial writing is needed. However, a plurality of recording LD power values for determining recording conditions are used for this recording. Therefore, it is not possible to use an optimum LD power detecting algorithm which has been conventionally used. Thus, a trial writing method for the phase-change optimum disc has not been established.
A density of an optical disc as a recording medium has been advantageously increased and also a speed of recording data in an optical disc has been advantageously increased. Further, in response to this, various recording methods suitable for the increased-density optical disc and increased recording speed have been proposed and embodied. One of these recording methods is a multi-pulse recording method.
The multi-pulse recording method will now be described. Information is optically recorded in and reproduced from an optical disc by an output of a semiconductor light-emitting device. In this recording, record marks representing the information are recorded in the optical disc and thus the information is recorded in the optical disc. According to the multi-pulse recording method, when one record mark is formed on the optical disc, a recording waveform to be input to the semiconductor light-emitting device for this purpose includes a series of discrete pulses having different light-emitting powers.
Advantages obtained from the multi-pulse recording method will now be described. This method may be applied to a PWM (Pit Width Modulation) method. In this PWM method, a pit (serving as a record mark) is formed on an optical disc and a width of each one of thus-formed pits represents the information. In the PWM method, it is essential to define a length and a width of the mark (pit) precisely in forming the mark. If a waveform which is one not divided into a series of discrete pulses is input to the semiconductor light-emitting device, heat concentrically stored at a position in the optical disc due to the light emission thereto may result in a tear-drop-shaped pit at the position. As a result, it is difficult to control the length and width of the mark precisely. In contrast to this, in the multi-pulse recording method, by inputting the waveform divided into the series of discrete pulses to the semiconductor light-emitting device, it is possible to effectively disperse the heat stored at the position in the optical disc due to the light emission. Thus, it is possible to precisely control the length and width of the pit at the position. Such an operation for controlling a shape of a record mark may be referred to as `recording pre-compensation`, hereinafter.
In particular, when the multi-pulse recording method is applied to the phase-change optical disc recording, by appropriately changing an output intensity of the semiconductor light-emitting device with time, it is possible to sharply cool the recording layer of the optical disc. Thus, it is possible to form the mark in a desired shape.
Japanese Patent Publication No.4-67260 discloses a light-output automatic-control apparatus as a semiconductor light-emitting device output-control apparatus which uses a semiconductor light-emitting device (semiconductor laser) and controls an output of the semiconductor light-emitting device. In the disclosed light-output automatic-control apparatus, a light detector is provided for receiving part of a light output from the semiconductor light-emitting device. Then, an output signal from the light detector is used as a feedback signal for the semiconductor light-emitting device output control.
This light-output automatic-control apparatus is not a semiconductor light-emitting device output-control apparatus in the multi-pulse recording method. However, in broad perspective, it is possible to apply the principle of the light-output automatic-control apparatus to a semiconductor light-emitting device output-control apparatus in the multi-pulse recording method. However, a semiconductor light-emitting device output-control apparatus in the prior art such as a typical light-output automatic-control apparatus can control and set only two light-emitting powers from the semiconductor light-emitting device, namely a read power and a write power. The read power is used when light is applied to an optical disc so as to reproduce information which was recorded therein. The read power may be referred to as a bias power. The write power is used to form a mark in the optical disc so as to record information therein.
In comparison to this, there are apparatuses in which it is necessary to control a semiconductor light-emitting device output using a number, more than two, of values of light-emitting power. Such an apparatus is, for example, a phase-change optical disc drive apparatus. For such an apparatus, it is not possible to use the principle of the above-described conventional semiconductor light-emitting device control apparatus which can control only two light-output powers.
Another possible problem in the conventional semiconductor light-emitting device control apparatus, such as the above-described light-output automatic-control apparatus using the light detector for obtaining the feedback signal for the relevant control operation, concerns a semiconductor light-emitting device output control speed depending on a performance of the light detector. If such an apparatus is used for controlling a light-emitting power to meet a recent demand for high-speed recording and the multi-pulse recording method, it is necessary to provide the light detector having a very high performance so as to constantly control the semiconductor light-emitting device appropriately.
Further, there is a recording pre-compensation method for performing recording pre-compensation according to the above-described multi-pulse recording method. This recording pre-compensation method is provided for a single recording speed. Therefore, if the recording speed is changed, such a change being recently demanded, optimum recording pre-compensation cannot be performed.